for National Geographic News
The two-headed monsters of myth may have a basis in reality. Two-headed snakes are rare but not unheard of, and one recently found in Spain is giving scientists an opportunity to study how the anomaly affects their ability to hunt and mate.
"We hear of one every several years," said Gordon Burghardt, a herpetologist at the University of Tennessee who has studied several two-headed snakes.
The snake in Spain, discovered near the village of Pinoso, is a two-month-old non-venomous ladder snake Elaphe scalaris. It is about eight inches (20 centimeters) long.
It's probably lucky it was capturedits chances of surviving in the wild are nil, said Burghardt.
"Just watching them feed, often fighting over which head will swallow the prey, shows that feeding takes a good deal of time, during which they would be highly vulnerable to predators," said Burghardt. "They also have a great deal of difficulty deciding which direction to go, and if they had to respond to an attack quickly they would just not be capable of it."
And that's assuming that both heads are hungry at the same time, and both are interested in pursuing the same prey.
"Having two heads would be a hindrance in the wild," agreed James Badman of Arizona State University. "It would be much harder to catch prey." Arizona State was home to a two-headed king snake that was found as a baby. It lived for nearly 17 years in captivity at the university.
Even in captivity, there are problems. Snakes operate a good deal by smell, and if one head catches the scent of prey on the other's head, it will attack and try to swallow the second head.
On the whole, though, they can do quite well in captivity, said Burghardt. Thelma and Louise, a two-headed corn snake at the San Diego Zoo that's now deceased, had 15 normal babies.
Anomaly, Not Evolution
Two-headed snakes typically occur in the same way that Siamese twins do. A developing embryo begins to split into identical twins but then stops part way, leaving the twins joined. Among humans, 75 percent of conjoined twins are stillborn or die within 24 hours.
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